package com.alstudio.net.protocol.xmpp.encode;

import java.io.*;

public class Base64 {

    static final char[] charTab = 
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray (); 

    /**
     * Create a base64 encoded string. 
     * @param data
     * @return encoded
     */
    public static String encode (byte [] data) {
        return encode (data, 0, data.length, null).toString ();
    }


    /** Encodes the part of the given byte array denoted by start and
        len to the Base64 format.  The encoded data is appended to the
        given StringBuffer. If no StringBuffer is given, a new one is
        created automatically. The StringBuffer is the return value of
        this method.
        @param data
        @param start
        @param len
        @param buf
        @return Encoded string
    */
    public static StringBuffer encode (byte [] data, int start, int len, StringBuffer buf) {

        if (buf == null) 
            buf = new StringBuffer (data.length * 3 / 2);

        int end = len - 3;
        int i = start;
        int n = 0;

        while (i <= end) {
            int d = ((( data [i]) & 0x0ff) << 16) 
                | ((( data [i+1]) & 0x0ff) << 8)
                | (( data [i+2]) & 0x0ff);

            buf.append (charTab [(d >> 18) & 63]);
            buf.append (charTab [(d >> 12) & 63]);
            buf.append (charTab [(d >> 6) & 63]);
            buf.append (charTab [d & 63]);

            i += 3;

            if (n++ >= 14) {
                n = 0;
                buf.append ("\r\n");
            }
        }


        if (i == start + len - 2) {
            int d = ((( data [i]) & 0x0ff) << 16) 
                | ((( data [i+1]) & 255) << 8);

            buf.append (charTab [(d >> 18) & 63]);
            buf.append (charTab [(d >> 12) & 63]);
            buf.append (charTab [(d >> 6) & 63]);
            buf.append ("=");
        }
        else if (i == start + len - 1) {
            int d = (( data [i]) & 0x0ff) << 16;

            buf.append (charTab [(d >> 18) & 63]);
            buf.append (charTab [(d >> 12) & 63]);
            buf.append ("==");
        }

        return buf;
    }


    static int decode (char c) {
        if (c >= 'A' && c <= 'Z') 
            return ( c) - 65;
        else if (c >= 'a' && c <= 'z') 
            return ( c) - 97 + 26;
        else if (c >= '0' && c <= '9')
            return (c) - 48 + 26 + 26;
        else switch (c) {
        case '+': return 62;
        case '/': return 63;
        case '=': return 0;
        default:
            throw new RuntimeException (new StringBuffer("unexpected code: ").append(c).toString());
        }
    }
                

    /** Decodes the given Base64 encoded String to a new byte array. 
        The byte array holding the decoded data is returned.
        @param s
        @return The real thingi
     */
    public static byte [] decode (String s) {

        int i = 0;
        ByteArrayOutputStream bos = new ByteArrayOutputStream ();
        int len = s.length ();
        
        while (true) { 
            while (i < len && s.charAt (i) <= ' ') i++;

            if (i == len) break;

            int tri = (decode (s.charAt (i)) << 18)
                + (decode (s.charAt (i+1)) << 12)
                + (decode (s.charAt (i+2)) << 6)
                + (decode (s.charAt (i+3)));
            
            bos.write ((tri >> 16) & 255);
            if (s.charAt (i+2) == '=') break;
            bos.write ((tri >> 8) & 255);
            if (s.charAt (i+3) == '=') break;
            bos.write (tri & 255);

            i += 4;
        }
        return bos.toByteArray ();
    }
}
